PHP - Reading File In A Textbox And Replacing The Information Within It After Saving

I'm using a php video web script which includes this buy_video.php file, which calculates the video uploader's earned amount, and insert's that amount in the 'u_paid_videos' table column named 'earned_amount', which appears in this file on line 73:

<?php
ob_start();

if (IS_LOGGED == false) {
    $data = array('status' => 400, 'error' => 'Not logged in');
    echo json_encode($data);
    exit();
}

if (!empty($_POST['id'])) {

    if (!is_array($_POST['id'])) {
        $id_array[] = $_POST['id'];
    } else {
        $id_array = $_POST['id'];
 	}

	// get cost video
	// get the default video price, to use if there is no per video play price
	$db->where('name', 'video_play_price');
	$db_cost = $db->getOne('config');
	$video_cost = (float)$db_cost->value;

	// the number of submitted videos - used to determine if all records were inserted
	$count_video = count($id_array);
	$user_id = $user->id;

	$wallet = (float)str_replace(',', '', $user->wallet);
	$balance = (float)str_replace(',', '', $user->balance);

	// add up the video prices
	$amount = 0;
	foreach ($id_array as $id) {

		$video_id = (int)PT_Secure($id);

		// get video data
		$video = $db->where('id', $id)->getOne(T_VIDEOS);
		// add the video play price if any, or the default price
		$amount += $video->video_play_price?$video->video_play_price:$video_cost;
	}

	// determine if the user has enough credits
	if( ($wallet >= $amount) OR ($balance + $wallet >= $amount) ) {
	//if( ($wallet >= $amount) OR ($balance >= $amount) ) {

		$db->startTransaction();

		$inserted_records = 0;
		foreach ($id_array as $id){

			$video_id = (int)PT_Secure($id);

			// get video data
			$video = $db->where('id', $id)->getOne(T_VIDEOS);

			// use the video play price if any, or the default price
			$video_cost_new = $video->video_play_price?$video->video_play_price:$video_cost;

			// credit the user 50% of the video cost
			$uploader_amount = $video_cost_new *0.50;



			// add data to paid table
			$insert_buy = $db->insert('u_paid_videos', [
				'id_user' => $user_id,
				'id_video' => $video_id,
				'session_key' => $_SESSION['session_key'],
				'video_play_price' => (string)$video_cost, // the cost at the time of purchase // this is the default video cost not the $video_cost_new
				'video_title' => $video->title, // storing the title
				'user_id_uploaded' => $video->user_id, // the user who uploaded the video
				'earned_amount' => $uploader_amount,
				]);

			// count successful inserted records
			if ($insert_buy) {
				$inserted_records++;
			}

			//update the 'balance' of the user who uploaded the video
			// get the user's record
			$userwallet = $db->where('id', $video->user_id)->getOne(T_USERS);

			// add to the balance
			$videouserwallet = $userwallet->balance+$uploader_amount;

			// update the record
			$db->where('id', $video->user_id);
			$update_balance = $db->update(T_USERS, [
				'balance' => number_format($videouserwallet, 1, '.', ''),
			]);
		}

		$update_wallet = null;
		$update_user_balance = null;


ETC .....................................................

Ultimately, I’m trying to integrate the buy_video.php file’s ‘$earned_amount’ into a web script’s existing transaction file.

Here are a couple of lines from that transaction file:

$this_day_video_earn = $db->rawQuery("SELECT SUM(amount - admin_com) AS sum FROM ".T_VIDEOS_TRSNS." c WHERE `time` >= ".$day_start." AND `time` <= ".$day_end." AND user_id = ".$pt->user->id);
$today_earn = $this_day_ads_earn[0]->sum + $this_day_video_earn[0]->sum ;

and

$trans = $db->where('user_id',$user->id)->orderBy('id','DESC')->get(T_VIDEOS_TRSNS);

That may not be enough info, but I’d like assistance changing those lines to:

$this_day_video_earn = $db->rawQuery("SELECT SUM(earned_amount) AS sum FROM “.T_VIDEOS.” c WHERE time >= “.$day_start.” AND time <= “.$day_end.” AND user_id = ".$pt->user->id);
  
  
  $trans        = $db->where('user_id',$user->id)->orderBy('id','DESC')->get(T_VIDEOS);

I tried those changes without success.
Any guidance/suggestions will be appreciated.

<?php
echo <<<_END
<form action="form.php" method="post">
<textarea name="textdata" cols="50" rows="20"></textarea>
<input type="submit" name="submit" value="CLICK ME">
<input type="hidden" name="submit_check" value="1">

</form>
_END;
function write(){
$fname="test.txt";
$fh=fopen($fname,'w');
$data=$_POST['textdata'];
fwrite($fname,$data);
fclose($fh);
}


if(isset($_POST['submit_check'])){
write();
}
?>